Slide fasteners of the woven-tape type generally comprise a pair of tapes which are adapted to be stitched to a garment or other fabric or nonfabric article or otherwise secured thereto, each of the tapes being provided along an edge with a row of coupling heads interdigitatable with the opposing row of coupling heads upon movement of the slide along the rows.
It is known to provide each row of coupling heads unitarily in a synthetic-resin monofilament or strand which is bent to form the coupling heads at respective turns of a coil or meander pattern so that a pair of shanks can extend away from each head and are joined to the shanks of adjacent coupling members (each formed by a head and a pair of shanks) at a respective bend, hereinafter referred to as a bight.
When the coupling element is woven into the respective support tape, which can consist of warp threads interwoven with weft threads lying in a double-weft configuration (i.e. two adjacent weft picks form each weft insertion), the weft threads can be looped around the warp in the region of the coupling element which can form a warp-like strand in the weave from which the heads project laterally along an edge of the tape.
The shanks of the coupling element can form double-weft insertions, when they lie adjacent one another, usually in a superposed configuration with one shank of each member lying directly over the other so that both shanks have a common projection in the slide-fastener plane.
The ground-weave weft threads can run to the regions of the coupling heads and the coupling members can be anchored to the support tape in part by warp threads interwoven with the double-weft insertions formed by the shanks.
While, as noted, the coupling elements can be either of the helical-coil type or the meander type, the preferred configuration for the present purposes is the coil.
A woven slide-fastener stringer half is described in German patent publication-Auslegeschrift DE-AS No. 17 85 363 in which the ground weft threads of the double-weft of the support tape lie adjacent the shanks of the coupling members. In a section orthogonal to the plane of the slide fastener, these ground wefts lie midway between the upper and lower shanks. Hence the shanks of each coupling member are substantially symmetrically disposed to either side of the plane of the tape and project therefrom by at least the thickness of the monofilament and half the height of the eye or loop formed by each coupling member at the respective head.
In this system, the two superposed shanks of each coupling member and the associated double-weft of the ground weft always similarly interwoven with the warp, i.e. are both passed over and under simultaneously by given warp threads. This is a consequence of the nature of the weft insertion by the weft-carrying needle looms used in fabricating these earlier stringers. The term as used herein refers to position during weaving. These "sheds" become yarn passes in the finished article.
While such techniques are effective in the formation of supple tapes from ordinary threads, they are found to pose problems when synthetic-resin coupling elements with thicknesses of 0.4 mm or more are used and which, by comparison with the ground weft threads and with the warp threads are relatively stiff and only limitedly bendable.
The integration of such coupling elements into the support tape has been found to be fraught with problems because of fluctuating and increased mechanical stress which can give rise to variations in the interhead spacing.
Frequently during the normal handling of the stringer, bending can result, i.e. in textile or manufacturing operations or even in use. With systems of the type described, the bending of the finished stringer or slide fastener can result in kinking of the coupling element which may be stressed during weaving and which can create problems when the slide fastener is to be sewn into a garment or the like.
Many of these problems have been traced to the fact that the coupling element is woven in place under the stresses generated by the weaving process so that relative movement of the coupling element and the support tape parts is not possible. When the tension on the tape is relieved, bending and buckling tendencies arise. Furthermore, the resulting slide fastener is not sufficiently flexible and soft for many modern applications and thus has not received wide-spread acceptance.
Greater success has been achieved with constructions of the type described in German patent publication-Auslegeschrift DE-AS No. 20 23 005 in which the double-pick weft insertions of the support tape is formed by ground weft threads while the synthetic-resin monofilament coupling element is formed in situ by coiling the monofilament on a mandrel so that it forms a warp strand which does not constitute any significant part of the weft but is locked in by the ground weft.
This system loses some of the advantages of double-weft insertion and does not utilize fully the possibilities of weft-insertion needle looms. This system also is not capable of truly high speed fabrication.